1. Technical Field
The present invention relates to an image forming apparatus and image forming system.
2. Related Art
An image forming apparatus such as a laser beam printer is already well known. There is an image forming apparatus including an intermediate transfer belt for carrying a developer image, a light-emitting member that emits light rays having a predetermined wavelength toward a surface layer of the intermediate transfer belt and a sensing member that senses the light rays reflected from the intermediate transfer belt.
There might be various objects for providing the light-emitting member and the sensing member as described above in the image forming apparatus. As an example, there is a case in which these members are provided for detecting the density of developer image carried on the intermediate transfer belt for adjusting the density of the image.
In such a case, a patch image (test pattern) as the developer image is developed when executing a control operation for controlling the density of the image, and the patch image is transferred to the intermediate transfer belt. Then, a light ray is emitted from the light-emitting member toward the intermediate transfer belt to which the patch image is transferred, and the emitted light ray (that is, incident light ray) is reflected from the intermediate transfer belt. Then, the reflected light rays are sensed by the sensing member, and the density of the patch image is detected on the basis of the detection result.
There is the intermediate transfer belt described above, which includes a metal layer and a surface layer which is a layer coated on the metal layer. As the intermediate transfer belt of this type, the intermediate transfer belt having a three-layer structure in which the metal layer is deposited on a base layer as a back layer, and the coated layer as the surface layer is coated on the metal layer is well known. Since the metal layer includes metal, the light reflection coefficient of the metal layer is larger than that of the coated layer. Therefore, when the light rays are emitted from the light-emitting member toward the intermediate transfer belt of this type, the light rays mainly pass through the coated layer and reflected from the metal layer.
In the image forming apparatus, different light rays having a wavelength different from the wavelength of the light rays emitted from the above-described light-emitting member (hereinafter, referred to as “different light rays” may be irradiated on the intermediate transfer belt. For example, as an example of the different light rays, there are light rays emitted from a component in the image forming apparatus, or light rays emitted from a fluorescent lamp provided in a room where the image forming apparatus is placed. When the light rays are emitted from the light-emitting member, and the reflected light rays thereof are sensed by the sensing member for the purpose of detecting the density of the developer image, the above-described reflected light rays of the different light rays reflected from the intermediate transfer belt (metal layer) are also received by the sensing member. Therefore, there is a problem that the different light rays received by the sensing member become noises, which results in deterioration of the sensing accuracy of the sensing member (that is, the sensing accuracy when sensing the light rays emitted from the light-receiving member).